I recently finished a couple of books that were for the educational market. For both of them the time frame was really short and the images had to be pretty specific, but they ended up being fun to work on. The main challenge for me with a short deadline and lots of images is that you have to design for the time you have. Usually I like to put in as many details as possible, but with these it is all about simplifying and making the images easy to understand. I've noticed that when I'm painting faster the over all colors end up being brighter.
This one is from Rudyard Kipling's "Just So Stories" for Compass Education.
These two were from "The Three Little Pigs" for Benchmark Education.